Systems and methods for determining defect characteristics of a composite structure

ABSTRACT

Systems and methods for determining a defect characteristic of a composite structure, such as defect density-per-unit area and/or cumulative. In one preferred embodiment, a method for determining a defect characteristic of a composite structure generally includes: determining a first distance from a first reference point of the composite structure to a defect; determining a second distance from a second reference point of the composite structure to the defect; using the first and second distances to establish a reference area of the composite structure; and considering each defect detected within the reference area and producing therefrom a defect characteristic representative of the composite structure.

COPYRIGHT NOTICE

A portion of the disclosure of this document contains material that issubject to copyright protection. The copyright owner has no objection tothe facsimile reproduction by anyone of the patent disclosure, as itappears in the U.S. Patent and Trademark Office patent files or records,but otherwise the copyright owner reserves all copyright rightswhatsoever.

FIELD

The present invention relates generally to the fabrication of compositestructures with material placement machines, and more particularly (butnot exclusively) to systems and methods for determining defectcharacteristics of a composite structure, such as defectdensity-per-unit area and/or cumulative defect width-per-unit area.

BACKGROUND

Composite structures have been known in the art for many years. Althoughcomposite structures can be formed in many different manners, oneadvantageous technique for forming composite structures is a fiberplacement or automated collation process. According to conventionalautomated collation techniques, one or more ribbons of compositematerial (also known as composite strands or tows) are laid down on asubstrate with a material placement machine. The substrate may be a toolor mandrel, but, more conventionally, is formed of one or moreunderlying layers of composite material that have been previously laiddown and compacted.

Conventional fiber placement processes utilize a heat source to assistin compaction of the plies of composite material at a localized nippoint. In particular, the ribbon or tow of composite material and theunderlying substrate are heated at the nip point to increase the tack ofthe resin of the plies while being subjected to compressive forces toensure adhesion to the substrate. To complete the part, additionalstrips of composite material can be applied in a side-by-side manner toform layers and can be subjected to localized heat and pressure duringthe consolidation process.

Unfortunately, defects can occur during the placement of the compositestrips onto the underlying composite structure. Such defects can includetow gaps, overlaps, dropped tows, puckers (i.e., raised regions in atow), and twists. In addition, there are foreign objects and debris(FOD), such as resin balls and fuzz balls, that can accumulate on asurface of the composite structure which must be detected, identifiedand eventually removed from the ply surface.

Composite structures fabricated by automated material placement methodstypically have specific maximum allowable size requirements for eachflaw, with these requirements being established by the productionprogram. Production programs also typically set well-definedaccept/reject criteria for maximum allowable number of (i.e., density)of defects-per-unit area and maximum allowable cumulative defectwidth-per-unit area.

To ensure that the composite laminates fabricated by fiber placementprocesses satisfy the requirements pertaining to defect size, thestructures are typically subjected to a 100% ply-by-ply visualinspection. These inspections are traditionally performed manuallyduring which time the fiber placement machine is stopped and the processof laying materials halted until the inspection and subsequent repairs,if any, are completed. In the meantime, the fabrication process has beendisadvantageously slowed by the manual inspection process and machinedowntime associated therewith.

Recently, systems have been developed that are capable of detecting,measuring, and marking individual defects in the composite structure.Exemplary systems and methods capable of accurately and reliablydetecting, measuring and/or marking defects in a composite structure aredisclosed in U.S. patent application Ser. No. 09/819,922, filed Mar. 28,2001, entitled “System and Method for Identifying Defects in a CompositeStructure”; U.S. patent application Ser. No. 10/217,805, filed Aug. 13,2002, entitled “System for Identifying Defects in a CompositeStructure”; and U.S. patent application Ser. No. 10/628,691, filed Jul.28, 2003, entitled “Systems and Methods for Identifying Foreign Objectsand Debris (FOD) and Defects During Fabrication of a CompositeStructure.” The entire disclosures of U.S. patent application Ser. Nos.09/819,922, 10/217,805, and 10/628,691 are each incorporated herein byreference as if fully set forth herein.

Although these inspection systems have worked well for their intendedpurposes, the inventors hereof have recognized that it would be evenmore beneficial to provide systems and methods that are capable ofdetermining a defect characteristic of a composite structure, such asthe composite structure's defect density-per-unit area and/or cumulativedefect width-per-unit area.

SUMMARY

Systems and methods for determining a defect characteristic of acomposite structure, such as defect density-per-unit area and/orcumulative defect width-per-unit area. In one preferred embodiment, amethod for determining a defect characteristic of a composite structuregenerally includes: determining a first distance from a first referencepoint of the composite structure to a defect; determining a seconddistance from a second reference point of the composite structure to thedefect; using the first and second distances to establish a referencearea of the composite structure; and considering each defect detectedwithin the reference area and producing therefrom a defectcharacteristic representative of the composite structure.

The features, functions, and advantages can be achieved independently invarious embodiments of the present inventions or may be combined in yetother embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will become more fully understood from thedetailed description and the accompanying drawings, wherein:

FIG. 1 is a schematic view of an exemplary composite structureillustrating linear and lateral distances to a defect in the compositestructure according to one embodiment of the invention;

FIG. 2 is a perspective view of a compaction roller having a code ringcoupled thereto for common rotation therewith and a photo sensorpositioned to monitor the code ring according to one embodiment of theinvention;

FIG. 3 is a schematic view of the code ring shown in FIG. 2;

FIG. 4 is a schematic view of a system according to one embodiment ofthe present invention;

FIG. 5 is a perspective view of a system according to another embodimentof the present invention;

FIG. 6 is a perspective view of a light source according to the systemembodiment shown in FIG. 5;

FIG. 7 is a perspective view of a system according to another embodimentof the present invention;

FIG. 8 is a perspective view of a light source according to the systemembodiment shown in FIG. 7;

FIG. 9 is an video frame capturing a pucker and a twist in a compositestructure;

FIG. 10 is a view of a computer display and user controls according toone embodiment of the present invention;

FIG. 11 is a view of an exemplary part model which may be imported fromexternal or third party software according to one embodiment of thepresent invention;

FIG. 12 is a view of the part model shown in FIG. 11 with a course gridoverlay according to one embodiment of the invention;

FIG. 13 is a view of the part model shown in FIG. 12 but with the coursegrid overlay repositioned to represent a change in orientation for thenew ply according to one embodiment of the invention;

FIG. 14 is a view of two computer displays simultaneously displaying thecomputer display shown in FIG. 10 and the part model and course gridoverlay shown in FIG. 13 according to one embodiment of the presentinvention;

FIG. 15 is a view of a computer display according to one embodiment ofthe present invention; and

FIG. 16 is a view of a computer display according to one embodiment ofthe invention.

Corresponding reference characters indicate corresponding featuresthroughout the several views of the drawings.

DETAILED DESCRIPTION OF THE EXEMPLARY EMBODIMENTS

According to one aspect, the invention provides a method for determininga defect characteristic of a composite structure, such as defectdensity-per-unit area and/or cumulative defect width-per-unit area. Inone embodiment, the method generally includes: determining a firstdistance from a first reference point of the composite structure to adefect; determining a second distance from a second reference point ofthe composite structure to the defect; using the first and seconddistances to establish a reference area of the composite structure; andconsidering each defect detected within the reference area and producingtherefrom a defect characteristic representative of the compositestructure.

Preferred embodiments of the invention provide methods for determiningfor a reference area or region of a composite structure one or more ofthe following defect characteristics: a total defect count, total defectwidth, defect density-per-unit area (i.e., number of defects-per-unitarea), cumulative defect width-per-unit area and/or defect location.Various embodiments allow these defect characteristics to be determinedas the composite structure is being fabricated, thereby eliminating theneed for manual inspection processes and the machine downtime associatedtherewith.

In one embodiment, the method generally includes determining a lineardistance to a defect along a course being laid by a material placementmachine; determining a lateral distance to the defect from a first endof the composite structure; using the linear and lateral distances toestablish a reference area; totaling defects within the reference area;dividing the defect total by the reference area to determine a defectdensity-per-unit area; determining a width for each defect within thereference area; totaling the widths of the defects within the referencearea; and dividing the width total by the reference area to determine acumulative defect width-per-unit area.

In the exemplary embodiment, the method includes determining both defectdensity-per-unit area and cumulative defect width-per-unit area.Alternatively, other embodiments can include determining any one orcombination of total defect count, total defect width, defectdensity-per-unit area, cumulative defect width-per-unit area and/ordefect locations. Further embodiments can include determining any one orcombination of total defect count, total defect width, defect density,cumulative defect width and/or defect locations for the entire compositestructure in which case a reference area need not necessarily beestablished.

FIG. 1 illustrates an exemplary composite structure 22, which isgenerally comprised of a plurality of adjacent tows or strips ofcomposite tape 24. The strips 24 typically include a plurality of fibersembedded in a resin or other material that becomes tacky or flowableupon the application of heat. The strips 24 are arranged on a worksurface, such as a table, mandrel, or other tool 26 (FIG. 4), andcompacted with a compaction roller 20 (FIGS. 2 and 5) to form thecomposite structure 22 according to an automated collation technique,such as that described in U.S. patent application Ser. No. 10/068,735,filed on Feb. 6, 2002, entitled “Composite Material Collation Machineand Associated Method for High Rate Collation of Composite Materials”.The contents of U.S. patent application Ser. No. 10/068,735 isincorporated herein by reference in its entirety as if fully set forthherein.

As shown in FIG. 1, eighteen courses or strips 24 have been completed bythe material placement machine. That is, the material placement machinehas made eighteen passes across a substrate. During each of the passes,the material placement machine has laid down a strip 24 on thesubstrate.

With further reference to FIG. 1, the sixth course 23 of the compositestructure 22 includes a defect 36 in the form of a tow gap.Additionally, or alternatively, the composite structure 22 can alsoinclude other types of defects such as overlaps, dropped tows, puckers,twists, and foreign objects and debris (FOD) with such defects beingcounted and measured by embodiments of the invention.

The dashed line 19 represents the linear distance along the sixth course23 to the defect 36. The dashed line 21 represents the lateral distanceto the defect 36 from a first end 11 of the composite structure 22.

Various methods may be used to determine linear distances along a courseto a defect detected in that course. In an exemplary embodiment, lineardistance to a defect along a course can be determined by multiplying thelinear velocity of the material placement head unit along the coursewith the amount of time that has lapsed between when the course beganand when the defect is detected.

When a defect is detected, a signal can be produced that not onlyindicates defect detection but may also trigger measurement and markingof the defect. Exemplary systems and methods capable of detectingdefects in a composite structure are described generally below and inmore detail in U.S. patent application Ser. No. 09/819,922, filed Mar.28, 2001, entitled “System and Method for Identifying Defects in aComposite Structure”; U.S. patent application Ser. No. 10/217,805, filedAug. 13, 2002, entitled “System for Identifying Defects in a CompositeStructure”; and U.S. patent application Ser. No. 10/628,691, filed Jul.28, 2003, entitled “Systems and Methods for Identifying Foreign Objectsand Debris (FOD) and Defects During Fabrication of a CompositeStructure.” The entire disclosures of U.S. patent application Ser. Nos.09/819,922, 10/217,805, and 10/628,691 are each incorporated herein byreference as if fully set forth herein.

The start and stop of a course can be determined using signals from themachine load cell which indicate whether or not pressure is beingapplied to the compaction roller 20 (FIGS. 2 and 5). Receipt of a“pressure on” signal from the machine load cell indicates that thecompaction roller 20 is in contact with the composite structure 22 andtherefore, that a course has been started. Receipt of a “pressure off”signal indicates that the compaction roller 20 is no longer in contactwith the composite structure 22, and therefore that a course has beencompleted. Accordingly, the time between course start and defectdetection can be determined by tracking the amount of time elapsingbetween receipt of the “pressure on” signal from the machine load celland the receipt of the signal indicating detection of a defect.

Alternatively, course start and stop can be determined by receipt of asignal from a device employing proximity sensors, lasers, or sounddetectors positioned for determining whether or not the compactionroller 20 is in contact with the composite structure 22.

In one embodiment, the linear velocity of the head unit is determined bydetermining the angular velocity of the compaction roller 20 andmultiplying the angular velocity by a circumference of the compactionroller 20. Alternatively, other methods can also be used to determinethe linear velocity of the head unit, such as by using a radar guncommonly used for law enforcement purposes in monitoring vehicularspeeds along roadways.

Referring to FIGS. 2, 3 and 5, the angular velocity of the compactionroller 20 can be determined by a code ring 1 coupled for common rotationwith the compaction roller 20. As shown, the code ring 1 includesalternating contrasting portions 2 and 3, such as alternating black andwhite segments. In FIG. 3, the code ring 1 includes an outer diameter 4of about 1.010 inches and an inner diameter 5 of about 0.844 inches,although other ring sizes can also be employed. In other embodiments,the contrasting portions can be provided directly on the compactionroller 20 (e.g., marked on, painted on, etc.), thereby eliminating theneed for the separate code ring 1.

With further reference to FIGS. 2 and 5, a photo sensor 7 (e.g., anoff-the-shelf photo diode, etc.) is positioned to monitor and capturereal-time images of the light-to-dark transitions of the code ring 1 asthe code ring 1 rotates along with the compaction roller 20. Bydetecting and counting the light-to-dark transitions of the ring 1, thecompaction roller revolutions can be counted and monitored. Thefrequency at which the light-to-dark transitions occur can be used toestablish the angular velocity of the compaction roller 20. Preferably,axial motion in the compaction roller 20 is minimized in order tomaintain the distance from the photo sensor 7 to the code ring 1constant, which, in turn, allows for more accurate determination of themachine head unit's linear velocity.

In another exemplary embodiment, the linear distance to a defect along acourse can be determined by counting the number (whole and fractional)of revolutions the compaction roller 20 makes from the start of thecourse to the defect and multiplying that number of revolutions by thecircumference of the compaction roller 20. By way of example, the photosensor 7 and code ring 1 can be used to count the number of revolutionsof the compaction roller 20 between receipt of the “pressure on” signalfrom the machine load cell and receipt of the signal indicating that adefect has been detected.

Various methods can also be employed to determine the lateral distancesto defects from the first end 11 of the composite structure 22. SeeFIG. 1. In one exemplary embodiment, lateral distance to a defect can becalculated by counting the total number of completed courses, notincluding the course in which the defect resides, and then multiplyingthe average width of a course by the number of completed courses. Thismethod is particularly effective for tape placement in which each courseis the same width, i.e., the width of the tape.

The total number of completed courses can be determined by tracking orcounting receipt of the pressure on/off signals from the machine loadcell. Receipt of a “pressure on” signal from the machine load cellindicates that the compaction roller 20 is in contact with the compositestructure 22 and has thus started a course. Receipt of a “pressure off”signal indicates that the compaction roller 20 is no longer in contactwith the composite structure 22 and has thus completed the course.

For fiber placement courses in which the width of each course may not beequal, the lateral distances to defects can be accurately determined byemploying a “software ruler.” More specifically, the lateral distancecan be determined by acquiring a digital image of at least the portionof the composite structure including the lateral distance; selecting apixel set from the digital image that represents the lateral distance;counting the number of pixels comprising the pixel set; and correlatingthe pixel count with correlation data (e.g., a predeterminedrelationship between pixel count and distance) to compute an indirectquantitative measurement for the lateral distance.

The width of a defect can be determined in a similar manner. After adigital image of the defect has been acquired, a pixel set is selectedfrom the digital image that represents the width of the defect. Thepixels comprising the pixel set are counted, and the pixel count is thencorrelated with correlation data (e.g., a predetermined relationshipbetween pixel count and distance) to compute an indirect quantitativemeasurement for the defect width.

Alternatively, defect width may be determined by multiplying the linearvelocity of the head unit (as determined in a manner described above) bythe amount of time required for the head unit to traverse the distanceseparating the opposed sides of the defect.

The reference area can be defined as any region of the compositestructure which is currently under inspection for defects and which hasa surface area about equal to the surface area of the reference area.Further, the reference area can be sized to include any suitable surfacearea, such as five square inches, one square foot, etc. In addition, thereference area can be sized in accordance with production requirementsto include only a portion of the composite structure. Alternatively,other embodiments can utilize a reference area corresponding in size tothe entire composite structure.

The reference area can be established in various ways. In one exemplaryembodiment, the reference area comprises any region of the compositestructure that is bounded by the linear and lateral distances to thepresently detected defect. For example, and referring to FIG. 1, areference area can be established for the defect 36 as the rectangularportion of the composite structure 22 defined by the dashed lines 19 and21 and the composite structure's first end 11 and lower side edge.

In another embodiment, the reference area comprises any region of thecomposite structure which is bounded by a predetermined linear distanceand a predetermined lateral distance.

In either of the aforementioned embodiments, the bounded reference areascan be tracked during the inspection, for example, in a lookup table.The lookout table might then be compared to a running tally of defects(e.g., running defect quantity and/or running defect width) during theinspection.

In yet other embodiments, the reference area is defined as the region ofthe composite structure which includes the preceding portion of thecourse in which the presently detected defect resides and all of thecompleted, preceding courses. For example, and referring to FIG. 1, areference area can be established for the defect 36 as the first fivecourses to the left of course 23 and that portion of the sixth course 23below the defect 36.

In further embodiments, the reference area is defined as a region of thecomposite structure which includes the preceding portion of the coursein which the presently detected defect resides and a predeterminednumber of completed courses immediately preceding the course in whichthe presently detected defect resides. For example, a reference area canbe established for the defect 36 as that portion of the sixth course 23below the defect 36 and the three courses (i.e., third, fourth and fifthcourses) to the immediate left of the sixth course 23 in FIG. 1.

In certain embodiments, a comparison is made between the cumulativedefect width-per-unit area and a maximum allowable cumulative defectwidth-per-unit area to determine whether a composite structure isacceptable or should be rejected. The maximum allowable cumulativedefect width-per-unit area can be set by production requirements. Whenthe cumulative defect width-per-unit area exceeds the maximum allowablecumulative defect width-per-unit area, the manufacturing process can behalted and/or an indicator of unacceptability can be provided, forexample, by a user interface 76 (FIG. 4) described below.

Additionally, or alternatively, certain embodiments include comparingthe defect density-per-unit area and a maximum allowable defectdensity-per-unit area to determine whether a composite structure isacceptable or not. The maximum allowable defect density-per-unit areacan be set by the production requirements. When the defectdensity-per-unit area exceeds the maximum allowable defectdensity-per-unit area, the manufacturing process may be halted and/or anindicator of unacceptability may be provided, for example, via the userinterface 76 (FIG. 4) described below.

An exemplary system 10 which can be used to detect defects in acomposite structure is illustrated in FIG. 4. As shown in FIG. 4, thesystem 10 includes at least one camera 12 and at least one light source14. The camera 12 is connected to a processor 66 for interpreting theimages the camera 12 captures, or to a storage device 64 for storing theimages, or both, as discussed more fully below.

The light source 14 is positioned to emit light for illuminating thecomposite structure 22. The illumination is reflected differently bydefects in the composite structure than from portions of the compositestructure that are defect free. For example, illumination reflecting offnon-defective portions of the composite structure 22, and light thatfails to reflect off of defects in the composite structure 22, or viceversa, creates visible images that can be captured by the camera 12.Details regarding systems and methods for identifying defects in acomposite structure during fabrication thereof are included inpreviously referred to U.S. patent application Ser. Nos. 09/819,922,10/217,805, and 10/628,691.

As shown in FIG. 4, the camera 12 is positioned near the compositestructure 22 so as to capture images of portion of the compositestructure being illuminated, which is typically immediately downstreamof the nip point at which a composite tow is joined with the underlyingstructure. Alternatively, and as shown in FIG. 5, a reflective surface16 may be positioned near the composite structure (the compositestructure is not shown in FIG. 5), and angled such that the reflectivesurface 16 reflects an image of the illuminated portion of the compositestructure. The camera 12 may be positioned to point toward thereflective surface 16 in order to capture close-range images of theilluminated portion of the composite structure from the reflectivesurface 16. More than one reflective surface 16 may also be utilized infurther embodiments of the invention in which the reflective surfaces 16cooperate in order to direct images of the illuminated portion of thecomposite structure to the camera 12.

A wide range of cameras can be used including commercially-availablecameras capable of acquiring black and white images. In one embodiment,the camera 12 is a television or other type of video camera having animage sensor (not shown) and a lens 13 through which light passes whenthe camera 12 is in operation. Other types of cameras or image sensorscan also be used, such as an infrared-sensitive camera, a visible lightcamera with infrared-pass filtration, a fiber optic camera, a coaxialcamera, Charge Coupled Device (CCD), or Complementary Metal Oxide Sensor(CMOS). The camera 12 can be positioned proximate the compositestructure 22 on a stand (not shown) or mounted to a frame 28 or similardevice.

In those embodiments that do not include a reflective surface 16, thecamera 12 may be mounted to the frame 28 by way of a bracket 30 andassociated connectors 32, as shown in FIG. 4. The connectors 32 may berivets, screws or the like that mount the camera 12 to the frame 28 in astationary position. Alternatively, the connectors 32 may be ahinge-type connector that permits the camera 12, light source 14, andassociated assembly to be rotated away from the composite structure 22.This embodiment is advantageous in situations where other parts of thematerial placement device, particularly the parts located behind thecamera 12 and associated assembly, must be accessed, such as formaintenance, cleaning, or the like.

FIG. 5 illustrates an alternative embodiment of the hinge-type connector32 that mounts the camera 12, reflective surface 16, light source 14,and associated assembly (e.g., camera assembly) to the frame 28 by wayof a bracket 30. A suitable fastener, such as a thumbscrew or any otherfastener that may be removed or loosened with relative ease, can beinserted through hole 34 and then tightened to secure the cameraassembly in place for operation. The fastener may be loosened orremoved, for example, to rotate the camera assembly away from thecompaction roller 20 and other parts of the fiber placement device.

With further reference to FIG. 4, a filter 15 can be placed on the lens13 for filtering light in a particular manner. In one embodiment, thefilter 15 is designed to filter light such that only the infraredcomponent or a certain infrared wavelength or range of wavelengths oflight can pass into the camera 12. In this manner, the filter 15prevents ambient visible light from entering the camera 12 and alteringthe appearance of the captured image.

Other methods of filtering light can also be used to achieve the same,or at least similar, result. For example, the camera may be designed toinclude a built-in filter of equivalent optical characteristics. Inaddition, the filter can be located between the camera lens 13 and imagesensor. Alternatively, the camera may include an image sensor that isonly sensitive in the infrared spectrum (e.g., an infrared-sensitivecamera), thus eliminating the need for the filter.

The light source 14 of the system 10 will now be described in moredetail. The light source 14 is positioned to emit light for illuminatingat least a portion of the composite structure 22.

In FIG. 4, the light source 14 is shown positioned at an oblique angle37 relative to the composite structure 22. The oblique angle 37 may beabout forty-five degrees, although other angles are possible dependingon the application. In addition, the light source 14 is also shownpositioned to emit light in a direction substantially perpendicular tothe direction of placement of the strips 24 in order to highlight thedefects 36, as described below.

Further, the system 10 may include more than one light source. Forexample, the embodiment of FIG. 5 includes two light sources 14positioned relative to the composite structure and compaction roller 20on either side of the reflective surface 16 and camera 12. Anotherexemplary embodiment that includes two light sources 14 is shown in FIG.7 in which two linear optical fiber arrays are positioned on opposedsides of the camera 12.

In FIG. 4, the light source 14 is adjustably positioned relative to thecomposite structure 22 by mounting or attaching the light source 14 to amounting apparatus 27. The mounting apparatus 27 can include a mainshaft 29, a secondary shaft 31, and a locking clamp 33 for quickly andaccurately adjusting the position of the light source 14. The mountingapparatus 27, in turn, can be attached to the frame 28, to the camera12, to the bracket 30, or to some other object that defines a commonposition for both the light source 14 and the camera 12 such that thelight source 14 and camera 12 maintain a constant spatial relationshiprelative to one another.

The quality and magnitude of the surface illumination of the compositestructure is greatly affected by ambient lighting and by thereflectivity of the material. Accordingly, embodiments of the inventionadvantageously employ an infrared light source to more effectivelyilluminate dark flaws on a dark background. In this regard, the lightsource 14 can be selected from an infrared light or another type oflight having an infrared component, such as a halogen light source (FIG.6) or other incandescent light sources (not shown). In otherembodiments, the light source 14 can also include a fluorescent lightsource (e.g., white light LEDs, low pressure/mercury filled phosphorglass tube, etc.), a strobe or stroboscopic light source, a noble gasarc lamp (e.g., xenon arc, etc.), metal arc lamp (e.g., metal halide,etc.) and a lasers (e.g., pulsed lasers, solid state laser diode arrays,infrared diode laser arrays, etc.). The light from the light source 14may also be pumped from through optical fibers to the point of delivery,such as is shown in FIG. 7.

In some embodiments, the light source 14 is operated at a power levelthat maximizes, or at least significantly increases, the infrared (IR)component of the light which works well for inspecting dark towmaterial, such as carbon. In this regard, exemplary power levels in therange of up to about one hundred fifty watts (150 W) in the wavelengthrange of about seven hundred nanometers to one thousand nanometers (700nm-1000 nm) have been sufficient. However, the particular power levelsand wavelengths for the light source will likely depend at least in parton the camera's speed and sensitivity, speed at which the material isbeing laid, delivery losses, and reflectivity of the material beinginspected, among other factors. For example, in other embodiments,wavelengths and power levels suitable for inspecting highly reflectivematerials can be employed.

In the embodiment shown in FIG. 4, the light source 14 may comprise aplurality of LEDs arranged in an array or cluster formation. In onespecific embodiment, the light source 14 includes 24 LEDs mounted in anarray upon a three-inch square printed circuit board.

In another embodiment shown in FIGS. 5 and 6, the light source 14includes four halogen light bulbs 38, although other quantities can alsobe used.

In the embodiment shown in FIG. 7, the light source 14 includes twolinear optical fiber arrays positioned on opposite sides of the camera12. The arrays emit light supplied from a remote source (not shown)through an optical fiber bundle 25. An illuminated linear array 14 isshown in FIG. 8.

Referring back to FIG. 5, the system 10 may further include a lightreflection element 18 located near the light source 14. The reflectionelement 18 include a series of light reflecting surfaces 40 (FIG. 6)that redirect the light towards the desired area to be illuminated. Thislevels the illumination across the surface and eliminates, or at leastsubstantially reduce, areas of intense light (i.e., hotspots) created bythe brightest portion of the light source 14. Hotspots are undesirablebecause hotspots prevent consistent illumination of the compositestructure, which may lead to errors during the processing of the imagescaptured by the camera 12.

The light reflection elements 40 are particularly advantageous forilluminating curved/contoured surfaces of composite structures becausethe redirection of the light permits a larger portion of the compositestructure to be evenly illuminated.

As shown in FIG. 6, the reflection element 18 is curved around the lightsource 14, such as in a parabolic shape. On the surface of thereflection element 18 that faces the light source 14, the reflectionelement 18 includes curved steps 40 substantially parallel to the lightsource 14. The distance between and curvature of the steps 40 can bechosen to be sufficient to provide even illumination from the sum of thetwo light sources, one on either side of the region of interest. Thisenables the reflection element 18 to provide more consistentillumination of the composite structure 22, which prevents, or at leastreduces, image processing errors due to inconsistent illumination of thecomposite structure 22. Alternatively, the shape and/or surfaceconfiguration of the reflection element 18 can be modified in other waysthat also produce consistent illumination and scattering of the lightproduced by the light source 14 over the desired portion of thecomposite structure 22.

In an exemplary embodiment, the reflection element 18 has an overallparabolic shape with seventeen parabolic curved steps 40 having a rangeof widths from about 0.125 inches at the outer edge of the reflectionelement 18 to about 0.250 inches at the center of the reflection element18. The reflection element 18 also has a uniform step height of about0.116 inches. In other embodiments, however, the reflection element maybe provided with different numbers of steps having different uniform orvarying widths and different uniform or varying step heights.

Furthermore, the reflection element 18 may be adjusted in order todirect the light produced by the light source 14 and scattered by thereflection element 18 toward the desired portion of the compositestructure. For example, as shown in FIG. 6, the reflection element 18 isadjustably mounted to the mounting apparatus 27 with fasteners 42. Theloosened fasteners 42 can move within slots 44 to correspondingly adjustthe angle of the reflection element 18 relative to the compositestructure. Once the reflection element 18 is positioned appropriately,the fasteners 42 are tightened to secure the reflection element 18 inthe desired position. Adjustments of the reflection element 18 can alsobe enabled by other methods, such as by electronic means that permitremote adjustment of the reflection element 18.

It has been observed that the composite structure 22 produces high glarewhen illuminated across the direction of placement of the strips 24 butproduces substantially less glare when illuminated along the directionof placement of the strips 24. The systems and methods of at least someembodiments exploit the high-glare/low-glare phenomenon by casting lightacross the top layer of the composite strips 24 in a directionsubstantially perpendicular to the direction of placement of the strips24. This produces a relatively large amount of glare on the top layer ofthe composite structure 22. The underlying layers, which producesignificantly less glare than the top layer because of theirorientation, will show through any gaps or other defects in the toplayer and thus be easily located. In addition, twists and other surfacedefects in the top layer will alter the orientation of the strips in thetop layer and thus correspondingly alter, i.e., decrease, the glare ofthe top layer at the defect location.

While the high-glare/low-glare phenomenon occurs when illuminated witheither visible light or infrared light, the filter 15 used in oneembodiment of the system 10 substantially removes the glare caused byambient light such that only the glare caused by the infrared lightsource is used to locate the defects. Accordingly, the filter 15 removesthe interference of ambient light as the composite structure 22 is beingexamined for defects.

In any of the system embodiments described herein, there may be one ormore cameras 12 and/or one or more light sources 14 with or withoutreflection elements 18 (collectively referred to as light sources,hereinafter). In addition, the one or more cameras 12 and/or the one ormore light sources 14 may be moveable relative to the compositestructure. The multiple cameras 12 and/or multiple light sources 14 andthe moveability of the camera(s) 12 and/or the light source(s) providessystem 10 flexibility in order to capture the most accurate images ofthe composite structure. Multiple and/or moveable light source(s) 14permit consistent and sufficient illumination of the desired portion ofthe composite structure, regardless of the shape of the compositestructure. Likewise, multiple and/or moveable camera(s) 12 enablecapturing an accurate image of any area of the composite structure,regardless of the shape of the composite structure. As such, themultiple and/or moveable light source(s) and/or camera(s) areparticularly advantageous when illuminating and capturing images of andcurved/contoured portions of composite structures. The multiple and/ormoveable light source(s) and/or camera(s) are also advantageous inilluminating and capturing images of composite strips having a widththat makes it difficult to illuminate and/or capture images of theentire strip, such that the position of the light source(s) and/orcamera(s) may be moved over the entire strip, and/or multiple stationarylight source(s) and/or camera(s) may be positioned to cover the entirestrip. Systems including moveable cameras and light sources aredescribed in detail in previously referred to U.S. patent applicationSer. No. 10/217,805.

As shown in FIG. 4, the system 10 can also include a marking device 62for marking the location of defects on the composite structure 22. Themarking device 62 may be attached to the frame 28 and be triggered by aprocessor 66 or similar device when a defect 36 is detected. The markingdevice 62 may spray or otherwise deposit an amount of ink, paint or thelike onto the composite structure 22 in those areas where defects 36 hasbeen detected. The markings on the composite structure 22 enables thelocation of the defects to be subsequently readily identified eitherautomatically or manually.

In the particular illustrated embodiment, the marking device 62 is aninkjet marking system that sprays a small spot of compatible ink of ahighly visible color onto the surface of the composite structure 22 atthe defect location to permit rapid access for repair and disposition.Alternatively, other marking methods can also be used, such as apump-fed felt-tip marker, spring-loaded marking pen, audio or visualalerts, and the like.

The camera 12 and/or the reflective surface 16, which along with thelight source 14 and any reflection element 18, can be mounted to thehead unit to allow the camera 12 to continuously capture real-timeimages of the composite structure 22 and the strips 24 as the head unitmoves across the composite structure 22 and the composite strips 24 arelaid down. If the composite structure 22 is not planar, the inspectionpoint should preferably be as close to the nip point as possible, asdescribed above. If the composite structure 22 is planar, the inspectionpoint can be located further from the placement head unit. In eithercase, the images can be stored in a memory device 64 for future analysisand/or processed immediately by the processor 66, as discussed morefully below.

FIG. 9 shows an exemplary raw or unprocessed camera image 68illustrating a contrast between potential defects, such as a pucker 75and a twist 77, and the remaining portions of the composite structure 22that are defect free. In the illustrated embodiment, the potentialdefects 75 and 77 are shown as black or gray areas, while the remainingnon-defective portions of the composite structure 22 remainsubstantially white 72. Once the potential defects are located, thedefects may be marked with the marker 62 and the linear and lateraldistances to the potential defects can be determined in a mannerdescribe above.

With further reference to FIG. 4, the processor 66 may receive theimages 68 from the camera 12 or from the memory device 64 in which theimages 68 have been stored. The processor 66 may then process andanalyze the images to facilitate the reliable detection of defects. Inat least one embodiment, the processor 66 and memory device 64 arecomponents of a conventional computer.

The system 10 may also include a user interface 76 that is incommunication with the processor 66. The user interface can beprogrammed such that it can run from a wide range of softwareapplications, including but not limited to DOS, Windows 98, Windows/NT,Windows 2000, Windows CE, Linux, Unix, and equivalents.

As shown in FIG. 10, the user interface 76 includes a display screen 80,such as on a computer monitor, and can also include an input device,such as a keyboard and mouse (not shown), for permitting an operator tomove a cursor about the display screen 80 and input various systemsettings and parameters. The display screen 80 can also betouch-sensitive for permitting the operator to input the desiredsettings by manually touching regions of the display screen.

The user interface 76 includes a window 81 in which an image 74 of thecomposite structure 22 is displayed for viewing by the operator or otheruser. The window 81 can also include a visual display 69 of defectlocation by course.

Although the image 74 can be the unprocessed camera image 68 (FIG. 9),the image 74 shown in FIG. 10 can also be a processed image that hasbeen binarized. During binarization, all shades of gray above apredetermined threshold value can be changed to white, while all grayshades below the threshold are changed to black to heighten the contrastof defects and improve the accuracy of defect detection. In otherembodiments, the binarization operation need not be performed butinstead the raw image, rates of change of the light levels in the rawimage, and/or color changes in the images can be used to identify thedefects.

The user interface 76 also provides user controls 78 for allowingvarious user inputs to the system. In the particular illustratedembodiment of FIG. 10, the user interface 76 allows adjustment to thebinarization threshold. Generally, the setting of the binarizationthreshold involves a tradeoff between the sensitivity with which defectsare detected and the resolution with which the defects are depicted. Inone embodiment, the binarization threshold is set to about 128 whichcorresponds to the mid-point on the 8-bit digitizing range of 0 to 255.However, other binarization threshold values can be employed dependingat least in part on the particular application, available lighting,camera settings, among other factors.

The user controls 78 also allow the user to adjust or shift the viewingarea within the window 81. During operation, the window 81 displaysreal-time moving video images of the illuminated portion of thecomposite structure 22 as the camera 12 and/or the reflective surface 18are moved relative to the composite structure 22.

The interface 76 can also allow the user to input the width of course ortow band 71 and maximum allowable cumulative gap width 73.

In addition to displaying images of the composite structure 22, thedisplay screen 80 also includes a defect table 82 which lists thediscovered defects and provides information for each defect, such aslocation, size, and the like.

The display screen 80 can also provide information (which can becontinuously updated) such as the number of defects 50, number ofcourses completed 52 (which may be determined by counting pressureon/off signals from the machine load cell as described above),cumulative defect width 54, and length of the current defect beingmeasured 56.

The display screen 80 can further include status indicators 84 thatnotify the user whether a particular image area is acceptable or notacceptable based on predefined criteria, such as maximum allowabledimensional parameters and tolerances.

The display screen can also include an indicator 85 that notifies theuser when the allowable cumulative defect width limit has been exceeded.

An exemplary embodiment includes importing a part model from external orthird party software (e.g., computer aided drafting (CAD) programs, workstation-based programs such as Unigraphics (UG) or CATEA, desktop PCapplications such as AutoCAD, etc.)

FIG. 11 illustrates an example of a complex part model 90 imported fromthird party software. As show in FIG. 12, a course grid overlay 92 canbe constructed for the imported part model 90 using the number ofcourses and the direction of travel that correspond to ply orientation.The diagrammatic concepts of linear and lateral distances 19 and 21 areillustrated in FIG. 12 to show defect 36 location on a surface morecomplex than the surface shown in FIG. 1.

After all courses for a ply have been laid, the course grid overlay 92′is repositioned to represent the change in orientation or direction oftravel for the new ply, as shown in FIG. 13. The interaction between theexternal or third party software and the software of the materialplacement machine can be designed to generate an entire set of grids(one for each ply of the part) in advance. These grids can be stored,with the appropriate grid being accessed, called up and positioned atthe start of each ply.

FIG. 14 illustrates another embodiment in which two computer displaysare employed for displaying and tracking the various defect data for theimported model 90. As shown, one monitor displays the computer display80 (previously described above in reference to FIG. 10) while the othermonitor simultaneously displays a computer display 180 of the part model90 and course grid overlay 92. The computer displays 80 and 180 can becontinuously updated to show positioning and locations of defects andflaws as they are detected through the vision system interface,described above.

FIG. 15 illustrates another embodiment 280 in which the display 180′ ofthe part model 90 and course grid overlay 92 are displayed within thewindow 81′ of computer display 80′.

FIG. 16 illustrates another embodiment 380 in which the display 80″ issuperimposed or positioned over a corner of the display 180″ includingthe part model 90 and course grid overlay 92.

Accordingly, embodiments of the present invention provide in-processvision-based inspection systems and methods capable of accurately andefficiently determining various defect characteristics such as totaldefect count, total defect width, defect density-per-unit area,cumulative defect width-per-unit area and/or defect locations.Embodiments of the invention allow composite structures to be fabricatedmore efficiently with fewer interruptions than conventional materialplacement systems which require manual inspections for and measuring ofdefects.

Embodiments of the invention permit rapid detection and measurement ofthe cumulative defect width-per-unit area, and tracking of the defectdensity-per-unit area. Because this defect information is relativelyimmediately available and manual measurement is not necessary, machinedown-time can be significantly reduced resulting in reducedmanufacturing costs and cycle times.

In addition, embodiments of the present invention allow for readyidentification of those composite structures that exceed maximumallowable tolerances pertaining to density and cumulative width ofdefects. This allows the fabrication process to be halted when maximumallowable tolerances are exceeded, thereby saving time and materialswhich would otherwise be lost during continued fabrication of anunacceptable composite structure.

Further, when too many composite structures are being rejected, anoperator can adjust the machines accordingly such that less material iswasted, less labor is expended, and less machine down time is incurredduring the fabrication process. Therefore, a lower cost compositestructure can be achieved on average.

Additionally, embodiments also enable improvements in the overallquality of the parts produced because defect density and cumulativedefect width can be determined more uniformly and reliably with thevarious systems and methods of the invention than with manualinspections.

While various preferred embodiments have been described, those skilledin the art will recognize modifications or variations which might bemade without departing from the inventive concept. The examplesillustrate the invention and are not intended to limit it. Therefore,the description and claims should be interpreted liberally with onlysuch limitation as is necessary in view of the pertinent prior art.

1. A method for determining a defect characteristic of a composite structure, the method comprising: determining a first distance from a first reference point of the composite structure to a defect; determining a second distance from a second reference point of the composite structure to the defect; using the first and second distances to establish a reference area of the composite structure; and considering each defect detected within the reference area and producing therefrom a defect characteristic representative of the composite structure.
 2. The method of claim 1, wherein considering each defect comprises summing all of the defects detected within the reference area to produce a total defect count for the reference area.
 3. The method of claim 2, further comprising dividing the total defect count by the reference area to produce a defect-per-unit area of the reference area.
 4. The method of claim 3, further comprising comparing the defect density-per-unit area to a maximum allowable defect density-per-unit area.
 5. The method of claim 1, wherein considering each defect comprises: determining a width for each defect detected within the reference area; and summing the widths of the defects within the reference area to produce a width total for the reference area.
 6. The method of claim 5, further comprising dividing the width total by the reference area to determine a cumulative defect width-per-unit area of the reference area.
 7. The method of claim 6, further comprising comparing the cumulative defect width-per-unit area to a maximum allowable cumulative defect width-per-unit area.
 8. The method of claim 5, wherein determining a width for each defect within the reference area comprises: selecting, from a digital image of at least a portion of the composite structure including the reference area, a pixel set for each defect within the reference area representing the width of the corresponding defect; determining a pixel count for each selected pixel set; and correlating each of the pixel counts with correlation data to determine the corresponding widths of the defects within the reference area.
 9. The method of claim 1, wherein determining a first distance comprises: determining a linear velocity of a material placement head unit; and using the linear velocity to determine the first distance.
 10. The method of claim 9, wherein using the linear velocity comprises: determining elapsed time between when a course started and when the detect is detected along the course; and multiplying the linear velocity by the elapsed time.
 11. The method of claim 9, wherein using the linear velocity comprises: determining elapsed time between when a first defect is detected along a course and when a second defect is detected along the course; and multiplying the linear velocity by the elapsed time.
 12. The method of claim 9, wherein determining a linear velocity comprises: determining an angular velocity of a compaction roller of the material placement head unit; and multiplying the angular velocity by a circumference of the compaction roller.
 13. The method of claim 12, wherein determining an angular velocity comprises detecting, counting, and establishing frequency of transitions between contrasting portions of a code ring coupled for common rotation with the compaction roller.
 14. The method of claim 1, wherein determining a first distance comprises: counting revolutions of a compaction roller from course start to detection of the defect; and multiplying the counted revolutions by a circumference of the compaction roller.
 15. The method of claim 14, wherein counting revolutions comprises detecting and counting transitions between contrasting portions of a code ring coupled for common rotation with the compaction roller.
 16. The method of claim 1, wherein determining a second distance comprises: summing courses completed to produce a total completed course count; and multiplying a predetermined course width by the total completed course count.
 17. The method of claim 16, wherein summing completed courses comprises tracking receipt of signals from a machine load cell indicating whether pressure is being applied to a compaction roller.
 18. The method of claim 1, wherein determining the second distance comprises: selecting, from a digital image of at least a portion of the composite structure including the second distance, a pixel set representing the second distance; determining a pixel count for the pixel set; and correlating the pixel count with correlation data to determine the second distance.
 19. The method of claim 1, wherein the reference area comprises a region of the composite structure bounded by the first and second distances.
 20. The method of claim 1, wherein the reference area comprises a region of the composite structure bounded by predetermined linear and lateral distances.
 21. The method of claim 1, further comprising implementing a user interface for displaying defect data and for allowing at least one user input.
 22. The method of claim 1, further comprising: importing a part model of a composite structure; overlaying a course grid on the part model; and displaying to a user the part model and course grid.
 23. The method of claim 22, further comprising: repositioning the course grid overlay when a new ply is started; and displaying to a user the part model and the repositioned course grid overlay.
 24. The method of claim 1, further comprising communicating with an inspection system inspecting the composite structure for defects.
 25. A method for determining a defect characteristic of a composite structure, the method comprising: determining a linear velocity of a material placement head unit along a course being laid; using the linear velocity to determine a linear distance from a first reference point along the course to a defect of the composite structure; and determining a lateral distance from a second reference point of the composite structure to the defect.
 26. The method of claim 25, wherein determining a linear velocity comprises monitoring revolutions of a compaction roller of the material placement head unit.
 27. The method of claim 25, wherein determining a linear velocity comprises: determining an angular velocity of a compaction roller of the material placement head unit; and multiplying the angular velocity by a circumference of the compaction roller.
 28. The method of claim 27, wherein determining an angular velocity comprises detecting, counting, and establishing frequency of transitions between contrasting portions of a code ring coupled for common rotation with the compaction roller.
 29. The method of claim 25, wherein determining a lateral distance comprises: summing courses completed to produce a total completed course count; and multiplying a predetermined course width by the total completed course count.
 30. The method of claim 29, wherein summing completed courses comprises tracking receipt of signals from a machine load cell indicating whether pressure is being applied to a compaction roller of the material placement head unit.
 31. The method of claim 25, wherein determining a lateral distance comprises: selecting, from a digital image of at least a portion of the composite structure including the lateral distance, a pixel set representing the lateral distance; determining a pixel count for the pixel set; and correlating the pixel count with correlation data to determine the lateral distance.
 32. A method for determining a defect characteristic of a composite structure, the method comprising: determining a linear velocity of a material placement head unit along a course being laid by monitoring revolutions of a compaction roller of the material placement head unit; using the linear velocity to determine a linear distance from a first reference point along the course to a defect of the composite structure; determining a lateral distance from a second reference point of the composite structure to the defect; using the linear and lateral distances to establish a reference area; and summing defects within the reference area to produce a total defect count for the reference area.
 33. The method of claim 32, further comprising dividing the total defect count by the reference area to determine a defect density-per-unit area of the reference area.
 34. The method of claim 32, wherein monitoring revolutions of a compaction roller comprises detecting, counting, and establishing frequency of transitions between contrasting portions of a code ring coupled for common rotation with the compaction roller.
 35. A method for determining a defect characteristic of a composite structure, the method comprising: determining a linear velocity of a material placement head unit along a course being laid by monitoring revolutions of a compaction roller of the material placement head unit; using the linear velocity to determine a linear distance from a first reference point along the course to a defect of the composite structure; determining a lateral distance from a second reference point of the composite structure to the defect; using the linear and lateral distances to establish a reference area; determining a width for each defect within the reference area; and summing the widths of the defects within the reference area to produce a width total.
 36. The method of claim 35, further comprising dividing the width total by the reference area to determine a cumulative defect width-per-unit area of the reference area.
 37. The method of claim 35, wherein monitoring revolutions of a compaction roller comprises detecting, counting, and establishing frequency of transitions between contrasting portions of a code ring coupled for common rotation with the compaction roller. 